Two dimensional (2D) materials are being actively pursued as possible successor materials to silicon. Two such 2D materials are graphene and metal chalcogenides, which have the form MX (“metal monochalcogenides”) or MX2 (“metal dichalcogenides”), where M is a metal atom, and Xis a chalcogenide that can be either S, Se, or Te.
Currently, 2D materials are formed using a variety of techniques. These techniques fall into two major categories, namely top-down methods and bottom-up methods. Top-down methods rely on exfoliation of bulk (three-dimensional-3D) forms of the materials in question (for example MoS2, or WS2, etc. . . . ) into their 2D form. For MoS2, such a method strips off thin layers of 2D MoS2 from the bulk 3D MoS2. The stripping process can be done via purely physical means, such as using cellophane tape to exfoliate the surface of the 3D material. The exfoliation can also be done electrochemically. In either case, the exfoliation technique yields extremely small amounts of the 2D materials at a time, e.g., on the order of square microns.
The bottom-up techniques seek to remedy the issue of only being able to generate small amounts of the desired 2D material, by initially growing a thin layer of the oxide of the metal, and subsequently processing it to arrive at a large-area layer of the 2D material. The most common film growth technique used for the bottom-up process has been chemical vapor deposition (CVD). While this technique can produce large areas of metal chalcogenides, the process is difficult to control to obtain monolayer growth of 2D material. In addition, the quality of material can vary greatly from run to run, which make subsequent use of the material as a substitute for silicon highly problematic.